Conventionally, conductive resin compositions such as conductive pastes, conductive paints, and conductive adhesives are used in various applications such as electronic components and electronic circuits. As conductive particles used in such conductive resin compositions, spherical or flaky silver (Ag) particles, copper (Cu) particles and the like are known. However, Ag has a problem of high price although it has very excellent conductivity, and Cu has a problem that the conductivity cannot be kept for a long time because it is easily oxidized and has poor corrosion resistance.
In contrast to the above, Japanese Patent Laying-Open No. 2008-111175 (PTD 1), Japanese Patent Laying-Open No. 2004-52044 (PTD 2), and Japanese Patent Laying-Open No. 2006-161081 (PTD 3) propose conductive particles in which the surfaces of Cu particles are covered with Ag. The conductive particles have characteristics of excellent conductivity, corrosion resistance, and moisture resistance. However, since Cu has a large specific gravity, conductive particles are easy to sediment in a conductive resin composition when Cu particles are used as core particles, and thus there is a fundamental problem of poor operability (handling easiness).
As a technique for solving the aforementioned problem of specific gravity, conductive particles obtained by covering the surfaces of silica particles having a small specific gravity with Ag, and conductive particles obtained by covering the surfaces of resin having a small specific gravity with Ag have been developed. For example, Japanese Patent Laying-Open No. 2001-23435 (PTD 4), Japanese Patent Laying-Open No. 61-257479 (PTD 5) and Japanese Patent Laying-Open No. 62-297471 (PTD 6) disclose techniques of precipitating metal on the surfaces of silica particles by using the electroless plating process after preliminarily subjecting the silica particles to a surface treatment using a silicon-based polymer compound having a reducing property or using a silane coupling agent. Also, for example, Japanese Patent Laying-Open No. 2006-228474 (PTD 7) discloses a composite conductive particle obtained by coating the surface of resin with a metallic conductive film, in which 70 to 90% of the surface area of the conductive film form rising protrusions.